1. Field of the Invention
The present invention relates to a communication terminal widely adopted in a navigation system mounted in a mobile unit.
2. Description of the Related Art
A car navigation system mounted in a vehicle which is a typical mobile unit is constructed so that a map is displayed on a display unit based on the present position of the vehicle whose position is measured and a mark showing the present position of my vehicle is superimposed and displayed on the map.
In the car navigation system, a position measurement unit is constructed of a GPS (Global Positioning System) receiver and a self-sustaining navigation sensor or the like for calculating the present position from a travel direction and a driving distance of the vehicle.
Also, map information for displaying the map on the display unit, attached information attached to the map information and various functional service are designed to receive supply from an information center existing outside the vehicle using a communication unit mounted in the vehicle.
In a navigation system for acquiring various information or receiving supply of various functional service by adopting a communication terminal in which the communication unit is mounted, it is desirably constructed so that without making a user aware of a connection state of the communication unit, information can be supplied (display, sound output) or operation can be advanced quick responsively.